Wire ropes traditionally comprise a plurality of wires or filaments that are wound or twisted into multi-wire strands, which in turn are twisted about each other to form a wire rope. Wire ropes are used in a variety of applications including drag lines, elevators, bridges, hoists, and marine tow ropes. Wire ropes are stressed and relaxed numerous times during their life cycle. They also undergo frictional stress to a certain degree in straight pulls but more so when they traverse a sheave or are wound onto a drum. The wires and strands are thus caused to move in relation to each other causing wear in the rope. Wire ropes are lubricated to promote unrestricted movement of the rope, minimal fatigue and frictional wear. Lubrication also provides protection against rust and corrosion.
Wire ropes are typically lubricated from the outside with a lubricating material such as an oil or a grease. It is common to lubricate a wire rope by dripping oil on it or pulling it through an oil bath. Thick coats of grease have also been applied to wire ropes from the outside with the hope that the grease will penetrate into the interior of the rope. These methods of lubrication are not long-term solutions because the lubricants evaporate or are wiped away during normal use.
In recent years, wire rope manufacturers have tried other methods to lubricate wire ropes. For example, a solid core made of a porous polymer, or other absorbent material, has been positioned in a wire rope. The solid core is made of a polymer and a lubricant. When the core is stressed, lubricating material is squeezed from the solid core. These lubrication techniques are time limited because of the finite lubricant supply in the cores. Attempts have been made to replenish the lubricant in rope cores by pouring additional lubricant over the rope or pulling it through a bath. These methods have not proven to extend the life of a wire rope for any appreciable amount of time.